- Galen (A.D. 129–201) : Galen refers to a Roman anatomist and physician who identified many of the major brain structures and described behavioral changes as a function of brain trauma. He associated each of Hippocrates ' four (4) humors with a temperament, thus creating a rudimentary theory of personality. Galen is the physician of the Emperor Marcus Aurelius in Rome and lived from 129 to 216. he is one of the most influential of the Greek physicians and he published a wide body of work that shaped Western biomedicine.